1. Field of the Invention
The invention relates to a semiconductor device and a method of producing the same. Particularly, the invention relates to a semiconductor device, such as one having a chip size package (CSP) structure, in which a surface of the semiconductor chip is covered by a layer of insulation material, such as a layer of polyimide, and a layer of aluminum (Al) forming electrodes or pads at the surface of the chip is not covered by the insulation material layer and is exposed.
As used herein, the term "semiconductor chip" means each of the individual semiconductor elements which are fabricated in a wafer and are not yet cut from the wafer as well as each of individual semiconductor elements which are cut from the wafer and separated from each other, unless specifically indicated.
2. Description of the Related Art
In a typical and conventional semiconductor device, an Al layer, which provides electrodes, is formed on a chip of silicon (Si), and it is common that wiring lines are attached to the electrodes of the Al layer by wire bonding.
In a semiconductor device of a CSP structure which has been developed to meet the latest needs of miniaturization of semiconductor devices and fabrication of components therein at a higher density, a polyimide layer as an insulation film is formed on a wafer in which many semiconductor elements (semiconductor chips) are fabricated and, on the polyimide layer, rerouting lines are formed, the rerouting line connecting an electrode or pad of conductor layer, typically Al layer, of each semiconductor chip through a via-hole formed in the polyimide layer to an external electrical circuit outside a package. In other words, the semiconductor device of a CSP structure requires a process for making rerouting lines on the insulation film of the chip so that the rerouting lines are electrically connected with the conductor layer of the chip.
In all of the cases where a wiring line is thus attached to an electrode or pad of an Al layer of a semiconductor chip, the electrodes or pads of the Al layer are exposed and, consequently, an oxidized film formed due to natural oxidation, so-called a "naturally oxidized film", is present on the surface of the Al layer. The presence of such an oxidized film is not preferable in that it increases a contact resistance between the electrode or pad and wiring line to be connected with it, and eventually makes electrical continuity between them defective. Accordingly, a treatment for the removal of such an oxidized film is needed.
In a process in which a wiring line is attached by wire bonding, a satisfactory electrical connection between an electrode (an Al layer) of a chip and the wiring line is established by using, for example, ultrasound or heat to mechanically break the oxidized film.
On the other hand, in a process in which rerouting lines are formed on an insulation film of a chip, satisfactory electrical connection between an electrode (an Al layer) of a chip and the rerouting line is established by removing the oxidized film by, for example, a treatment in which positive ions, typically Argon ions (Ar.sup.+), in a plasma are accelerated and are bombarded against the surfaces of the respective chips of a target wafer (ion bombardment or ion milling) is carried out prior to the formation of a metallic thin film for the rerouting lines by sputtering.
However, such an ion bombardment simultaneously has also effect on the surface of the polyimide layer as an insulation film exposed at the top of the wafer, resulting in breakage of some of bonds between atoms in the polyimide layer and loss of its insulation properties. Consequently, the insulation resistance of the polyimide layer can be largely decreased.
Such a problem is not desired in a semiconductor device having a CSP structure, but can commonly arise with a semiconductor device if the device generally has an insulation film, such as a layer of polyimide, covering the surface of a semiconductor chip, and an Al layer for electrodes or pads is not covered by the polyimide layer and is exposed.